This invention relates to hydraulically actuated pumps and particularly to subsurface oil well pumps of the type having a hydraulically actuated engine connected to reciprocate a downhole pump. More specifically, this invention comprehends improvements in hydraulically actuated engines for downhole pumps and in particular to an improved control valve assembly which controls the flow of power fluid to an engine piston thereof which in turn is connected to reciprocate a pump piston of a downhole pump to which the engine may be attached. This invention provides a new, improved valve assembly for a hydraulically actuated engine of a downhole pump assembly, and is particularly adapted for use in the type of pump disclosed in several prior art patents such as U.S. Pat. No. 3,703,926, for example.
An important benefit that is derived by combining my new improved engine with various prior art production pumps is that the valve rod or control valve can be made much larger in diameter thereby making it possible to increase the operating speed as well as the rate of produced fluid/per stroke, all of which represents unexpected improvements in operation of both the engine end as well as the pump end of the pump assembly. Those skilled in the art, having fully digested this entire disclosure, will appreciate that my improved hydraulic engine can advantageously be incorporated into and combined with numerous downhole pump ends other than the specific examples cited herein.
Usually the entire valve assembly of a hydraulically actuated engine assembly is positioned at the uppermost end of the engine therefor, all of which is positioned at the uppermost end of the downhole pump assembly. Accordingly the term "downhole pump assembly" means an engine end and a pump end with the engine end having a valve assembly connected to supply power fluid to the engine piston in such a manner that the engine piston strokes or reciprocates a connecting rod connected to a pump piston of a downhole pump.
The valve assembly of the engine end is housed within a main body thereof within which there is mounted a fixed annular member having an axial bore through which there reciprocatingly extends a control rod. The upper end of the control rod is hollow and extends above the engine piston to which it is directly connected. The engine and pump pistons are interconnected by a connecting rod.
The engine piston has power fluid passageways formed therein and connected to the hollow control rod for power fluid being received under the engine piston and thereby cyclicly forcing the piston to reciprocate upwards. A control sleeve is fixed within the main body of the engine, with an annulus provided between the control sleeve and the fixed annular liner member for reciprocatingly receiving the annular engine control valve therein.
Those skilled in the art will appreciate that the configuration of the engine valve, control sleeve, fixed annular member, and control rod are of a design to control the flow of fluid to and from the engine piston so that the control rod strokes up and down in response to the reciprocation of the engine piston, or vice versa, as will be better appreciated later on as this disclosure is more fully digested. In a single action pump, the hydrostatic head of the fluid produced by the pump end can be utilized to force the engine piston back down.
In some types of hydraulically actuated downhole pump engines, after the pump assembly has been in operation for some time, the pump assembly will stop, with both pistons (engine and pump) remaining in the uphole position and nothing, up until this invention, cures this malfunction other than pulling the pump assembly from the well bore and replacing the worn parts. This heretofore unexplained malfunction is especially prevelent in engines of the type seen in the Coberly, U.S. Pat. No. 2,081,223 and McArthur, U.S. Pat. No. 3,849,030, and therefore reference is made to these two patents as being examples of prior art pump assemblies which are greatly improved by the present invention.
This type of malfunction of prior art downhole pump assemblies usually is incorrectly attributed to an unduly worn pump engine, which is true to some extent, however, the stuck or stalled engine usually is not badly worn at all, except as will be discussed hereinafter, because most of its usful life still remains and advantageously can be used when the engine valve assembly is made in accordance with this invention. Hence the useful life of these and other similiar prior art engine and pump assemblies can be greatly extended by incorporation of the present invention thereinto.
In prior art valve assemblies, such as cited herein, the top end of the control valve strikes its adjacent confronting stop member each upstroke of the pump. In some new prior art valve assemblies, these coacting abutting surfaces are imperfect due to normal fabrication techniques, and leakage will occure thereacross which allows the control valve assembly to operate while the engine parts are new, but when the top end of the control valve has become worn to a degree that firmly seats the control valve against its stop and thus leakage across the control valve and stop member is precluded due to this progressive wear, the engine control valve will remain seated agaist its respective stop member thereby bringing the operation of the pump assembly to a stop. Hence the pump assemble has become "locked up" due to the upper terminal end of the control valve and the lower terminaend of the stop member becomming a closed valve type structure which prevents fluid flow thereacross each time the control valve engages the upper stop therefor. This invention teaches means by which this malfunction is obviated by the provision of a flow path that extends from the interior of the control valve to the exterior thereof whereby the pressure differential across the control valve is returned to a value that sustains continuous operation of the engine assembly.
This phenomna is particularly evident in prior art engines, such as the Coberly pump, cited above, because there is a micro thread formed on the control valve by the parting tool used during the manufacturing process, and during initial operation of the engine this imperfection allows high pressure power fluid flow across the interface at the top end of the control valve and its stop member. During this initial running operation, the control valve repeatedly pounds the top control valve stop each stroke of the pump assembly, until the micro threads are polished or abraded away, and, when they are gone, a positive seal is formed at the polished ends of the control valve and its confronting stop member.
This inadvertent formation of a valve and seat from coacting parts that never were intended to be a valve device reduces the available downward force on the control valve because the net area of the main valve's upper end (see 65, FIG. 14 of the Cobely U.S. Pat. No. 2,081,223 and 35 of FIG. 2 of the McArthur U.S. Pat. No. 3,849,030) no longer is subjected to the force of the power fluid. Accordingly, the engine stalls, or ceases operation, and must be removed from the borehole and repaired which is a costly undertaking, especially in view of the pump assembly being relatively new with a long operating life left were it not for the intervening malfunction that is brought about for the reasons cited above.
Applicant has discovered that this malfunction can be avoided by modification of the control valve of a hydraulically actuated engine in accordance with this disclosure.